This invention relates to an adaptive differential pulse code modulation (ADPCM) circuit in which PCM encoding and ADPCM encoding are alternately repeated, and more particularly an improved ADPCM decoding circuit in which quantized noises do not accumulate.
An ADPCM is described in detail in "Proceedings of IEEE", April, 1980, pages 488 to 525, and an improved ADPCM free from transmission line bit error is described in detail in "Proceedings of ICASSP" published by IEEE, May, 1982, pages 960 to 963.
As will be described later in more detail when a plurality of ADPCM encoder/decoders are connected in cascade, a problem that the degradation of the characteristic accumulates has hitherto arisen.